Method of controlling vehicle hydraulic brake system

ABSTRACT

A method of controlling a pump-driven type vehicle hydraulic brake system which can suppress pulsation of brake hydraulic pressure and makes it possible to accurately and quickly apply brake hydraulic pressure is provided. Using an equation between the pressure rising speed of the hydraulic pressure in the master cylinder and the approximate required driving force of the motor, the driving force of the motor is set from the pressure rising speed of the detected hydraulic pressure. The driving force of the motor is controlled to minimize the hydraulic pressure difference between the brake hydraulic pressure increased by the preset driving force and the hydraulic pressure in the master cylinder, thereby bringing the brake hydraulic pressure substantially close to the hydraulic pressure in the master cylinder. Only for the remaining hydraulic pressure difference, the motor driving force is controlled with a small control output to quickly and precisely apply brake hydraulic pressure while suppressing pulsation of the brake hydraulic pressure.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a method of controlling a vehiclehydraulic brake system provided with a pump for producing brakehydraulic pressure.

[0002] In recent years, in order to realize sophisticated vehiclebehavior control and a light brake operation feeling, as described e.g.in patent publication 2590825, a vehicle hydraulic brake system isemployed in which a pump as a hydraulic pressure source for producingbrake hydraulic pressure is provided and a motor for driving the pump isactuated based on a detection signal of a brake operating forcedetecting means for detecting the operating force of a brake operatingmember.

[0003] Among such pump-driven type brake systems, there are ones inwhich a master cylinder for producing hydraulic pressure correspondingto the operating force applied to the brake operating member is incommunication with wheel cylinders through an on-off valve by way of aso-called master cylinder passage, and if the pump is not operatingnormally, the hydraulic pressure in the master cylinder is transmittedas brake hydraulic pressure by opening the on-off valve to provide afailsafe function.

[0004] For such pump-driven type brake systems, a method of controllingthe driving force for the pump-driving motor with the brake hydraulicpressure corresponding to the brake operating force as detected by thebrake operating force detecting means as a target value is oftenemployed. For such controls of the motor driving force, PID control isordinarily employed.

[0005] In the control method of such a pump-driven type vehiclehydraulic brake system, there is a delay in response after the brakeoperating force has been detected by the brake operating force detectingmeans until the pump-driving motor is actuated, so that rise of thebrake hydraulic pressure is slow. Thus, in the initial period ofoperation of the brake operating member, a large difference in hydraulicpressure is produced between the control target value of the brakehydraulic pressure and the actual brake hydraulic pressure.

[0006] Thus, in the above-described conventional control method, if thecontrol output of the motor driving force is increased corresponding tothe hydraulic pressure difference, the brake hydraulic pressure in thewheel cylinders pulsates due to brake fluid discharged from the pump, sothat no smooth control is possible. Also, if the control gain is reducedto suppress such a pulsation of the brake hydraulic pressure, a speed atwhich brake hydraulic pressure follows the target pressure slows down,so that the driver feels a delay in the braking effect. During abruptbraking, it is possible that the braking effect will not appear in time.

[0007] An object of this invention is to provide a control method of apump-driven type vehicle hydraulic brake system which can suppresspulsation of brake hydraulic pressure and makes it possible toaccurately and quickly apply brake hydraulic pressure.

SUMMARY OF THE INVENTION

[0008] According to this invention, there is provided a method ofcontrolling a vehicle hydraulic brake system comprising a wheelcylinder, a pump for producing brake hydraulic pressure by supplyingbrake fluid into the wheel cylinder, a motor for driving the pump, afluid passage for bringing the pump and the wheel cylinder intocommunication with each other, a brake hydraulic pressure detectingmeans for detecting the brake hydraulic pressure in the wheel cylinder,a brake operating member, and a brake operating force detecting meansfor detecting the operating force applied to the brake operating member,and adapted to detect the brake operating force by the brake operatingforce detecting means and control the driving force of the motor withthe brake hydraulic pressure corresponding to the detected brakeoperating force used as a target value, characterized in that anequation showing the relation between the rising speed of the brakeoperating force and the driving force of the motor required to cause thebrake hydraulic pressure to follow the brake operating force isdetermined beforehand, and the driving force of the motor is preset fromthe rising speed of the detected brake operating force by use of theequation, and the driving force of the motor is controlled so as todecrease the hydraulic pressure difference between a target brakehydraulic pressure and the brake hydraulic pressure which is estimatedto rise by the preset driving force or the actual brake hydraulicpressure that has been increased by the preset driving force of themotor.

[0009] That is to say, by determining an equation showing the relationbetween the rising speed of the brake operating force and the requireddriving force of the motor beforehand, setting the driving force of themotor from the rising speed of the detected brake operating force by useof the equation, controlling the driving force of the motor to decreasethe hydraulic pressure difference between the estimated value or actualvalue of the brake hydraulic pressure to bring the brake hydraulicpressure substantially close to the target value with the set drivingforce, and only for the remaining hydraulic pressure difference,controlling the motor driving force with a small control output, it ispossible to quickly and smoothly cause the brake bydraulic pressure tofollow the target value.

[0010] This control method for the vehicle hydraulic brake system canalso be employed for a brake system in which a master cylinder forproducing hydraulic pressure corresponding to the operating forceapplied to the brake operating member is provided, and a master cylinderpassage for communicating the master cylinder with the wheel cylinderthrough an on-off valve is provided to transmit the hydraulic pressureproduced in the master cylinder by selectively opening and closing theon-off valve in the master cylinder passage.

[0011] By adding the value of the brake hydraulic pressure itself to theequation between the rising speed of the brake operating force and thedriving force of the motor as a parameter, since the required drivingforce of the motor slightly changes with the level of the brakehydraulic pressure itself, it is possible to increase the accuracy ofcontrol for bringing the brake hydraulic pressure close to the targetvalue with the set driving force.

[0012] If a master cylinder for producing hydraulic pressurecorresponding to the operating force applied to the brake operatingmember is provided, means for detecting the hydraulic pressure producedin the master cylinder is provided, and the hydraulic pressure in themaster cylinder detected by the master cylinder hydraulic pressuredetecting means can be used as a brake operating force in the control.

[0013] Other features and objects of the present invention will becomeapparent from the following description made with reference to theaccompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a circuit diagram showing a brake system to which isapplied a control method of a first embodiment;

[0015]FIG. 2 is a flowchart showing a control method of Example 1 forthe brake system of FIG. 1;

[0016]FIG. 3A is a graph showing control results of Example 1;

[0017]FIG. 3B is a graph showing control results of Comparative Example;

[0018]FIG. 4 is a flowchart showing a control method of Example 2 forthe brake system of FIG. 1;

[0019]FIG. 5 is a circuit diagram showing a brake system to which isapplied a control method of the second embodiment; and

[0020]FIG. 6 is a flowchart showing a control method of the brake systemof FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] Hereinbelow, with reference to the drawings, the embodiments ofthis invention are described. FIG. 1 shows a vehicle hydraulic brakesystem to which is applied the control method of the first embodiment.In this brake system, a pump 2 as a hydraulic pressure source driven bya motor 1 is mounted in a fluid passage 5 through which a reservoir tank3 and a wheel cylinder 4 communicate with each other. A master cylinder8 is coupled to a brake pedal 7 as a brake operating member through abooster 6. The hydraulic pressure produced in the master cylinder 8 isdetected as a brake operating force by a below-described pressure sensor13 a.

[0022] Also, the master cylinder 8 and the wheel cylinder 4 communicatewith each other through a solenoid valve 9, which is an on-off valve, byway of a master cylinder passage 10. Between the wheel cylinder 4 andthe reservoir tank 3, a relief passage 12 for brake fluid is alsoprovided in which is mounted a solenoid valve 11.

[0023] In the master cylinder passage 10, pressure sensors 13 a, 13 bfor detecting the hydraulic pressures in the master cylinder 8 and thebrake hydraulic pressure in the wheel cylinder 4, respectively, aremounted. To the brake pedal 7, a stroke sensor 14 for detecting itsdepressing amount is mounted. Detection signals from these sensors 13 a,13 b and 14 are inputted in a controller 15. Based on these detectionsignals, actuations of the motor 1 and solenoid valves 9 and 11 arecontrolled.

[0024] In a normal state, the solenoid valve 9 is closed, so that themaster cylinder 8 and the wheel cylinder 4 are shut off from each other.When the controller 15 detects depressing of the brake pedal 7 by thestroke sensor 14, it closes the solenoid valve 11 in the relief passage12, activates the motor 1 simultaneously, and controls the driving forceof the motor 1 in the below-mentioned manner to supply brake fluid inthe reservoir tank 3 to the wheel cylinder 4 by the pump 2 to generatebrake hydraulic pressure.

[0025] But if the amount of brake fluid supplied by the pump 2 becomesinsufficient for some reason and the controller 15 judges that the brakehydraulic pressure detected by the pressure sensor 13 b is insufficient,the controller opens the solenoid valve 9 in the master cylinder passage10 to transmit hydraulic pressure in the master cylinder 8 to the wheelcylinder 4 to produce a sufficient brake hydraulic pressure.

[0026] In either of the above cases, when the controller 15 detectsrelease of the brake pedal 7, it opens the solenoid valve 11 in therelief passage 12 to release the braking force and return brake fluidsupplied to the wheel cylinder 4 to the reservoir tank 3.

[0027] Hereinbelow, the control method of the first embodiment isdescribed with reference to two Examples. In this control method, thedriving force W of the motor 1 is controlled by the controller 15, andan estimate control and a feedback (FB) control are combined.

EXAMPLE 1

[0028]FIG. 2 shows a flowchart of the control method of Example 1.First, in the estimate control, the hydraulic pressure P_(M) in themaster cylinder 8 as the brake operating force detected by the pressuresensor 13 a is entered in the controller 15. The latter determines thepressure rise speed dP_(M)/dt of the hydraulic pressure P_(M) from thisinput signal, and calculates the driving force W_(S) of the motor by thefollowing equation:

W _(S) =C ₁·(dP _(M) /dt)  (1)

[0029] Equation (1) is one formulated by experientially finding therelation between the pressure rise speed of the hydraulic pressure P_(M)in the master cylinder 8, which reflects the degree of requirement forthe braking force by the driver, and the driving force W of the motornecessary to produce the required braking force. C₁ is a proportionalconstant. That is to say, by actuating the motor with the driving forceW_(S) calculated by use of the equation (1), the brake hydraulicpressure P_(W) in the wheel cylinder 4 as control results is increasedto a value close to the target hydraulic pressure P_(M) in the mastercylinder 8. In this Example, the number of times of control in theestimate control was one time only.

[0030] Next, in the feedback control, the hydraulic pressure P_(M) inthe master cylinder 8 as detected by the pressure sensor 13 a and thebrake hydraulic pressure P_(W) in the wheel cylinder 4 as detected bythe pressure sensor 13 b are entered moment by moment into thecontroller 15. The latter calculates the hydraulic pressure differenceΔP between the hydraulic pressure P_(M) and the brake hydraulic pressureP_(W), and calculates the motor driving force increment ΔW for thecalculated hydraulic pressure difference ΔP with a gain function f ofPID control, and outputs it. The brake hydraulic pressure P_(W) as thecontrol results of the estimate control and feedback control is fed backinto the controller 15 by the pressure sensor 13 b to continue thefeedback control.

[0031]FIG. 3A shows results in which the control method of Example 1,which is a combination of the estimate control and feedback control, iscarried out in the brake system shown in FIG. 1 and FIG. 3B shows theresults of the conventional control method in which only the feedbackcontrol by the PID control is performed.

[0032] In the control method of Example 1, in which the estimate controlis also used, compared with the conventional control method, the risingspeed of the brake hydraulic pressure P_(W) was markedly high, andsmoothly followed the hydraulic pressure P_(M) in the master cylinder 8as the target. On the other hand, in the conventional control method,not only was the rising speed of the brake hydraulic pressure P_(W)slow, but due to a large control output to the pump 2, the brakehydraulic pressure P_(W) pulsated, so that smooth control was notpossible.

EXAMPLE 2

[0033]FIG. 4 shows a flowchart of the control method of Example 2. Inthis control method, the number of times of control in the estimatecontrol was plural, and the proportional constant C₁ in the equation (1)between the pressure rise speed dP_(M)/dt of the hydraulic pressureP_(M) in the master cylinder 8 and the driving force W_(S) of the motorwas made as a function g of the brake hydraulic pressure P_(W) as shownin the following equation. The control period in the estimate controlwas 10 times that in the feedback control.

C ₁ =g(Pw)  (2)

[0034] For the feedback control, the input of the brake hydraulicpressure P_(W) from the pressure sensor 13 b was corrected with theestimated rising amount δP_(WS) of the brake hydraulic pressure P_(W) bythe preset motor driving force W_(S) as the output of the estimatecontrol as shown below.

[0035] For the driving force W_(S) calculated by use of equation (1),the estimated rising amount δP_(WS) of the brake hydraulic pressureP_(W) is calculated by the following equation:

δP_(WS) =C ₂ ·W _(S)  (3)

[0036] Equation (3) is determined from the relation between the drivingforce W of the motor 1 and the delivery speed of the pump 2 and can beobtained beforehand by experiments or calculation. C₂ is a proportionalconstant.

[0037] Next, the estimated rising amount δP_(WS) calculated in equation(3) is added to the input value of the brake hydraulic pressure P_(W)from the pressure sensor 13 b to determine the estimated brake hydraulicpressure P_(WS), which is an expected pressure rise by the estimatecontrol, and feedback control is carried out for the hydraulic pressuredifference ΔP between the input value of the hydraulic pressure P_(M) inthe master cylinder 8 from the pressure sensor 13 a and the estimatedbrake hydraulic pressure P_(WS). Other procedures are the same as inExample 1.

[0038] At timings at which no estimate control is carried out, since thedriving force W_(S) is not outputted, the estimated rising amountδP_(WS) is zero. Thus, the feedback control at these timings issubstantially the same as in Example 1, and feedback control is carriedout for the hydraulic pressure difference ΔP between the hydraulicpressure P_(M) as inputted and the brake hydraulic pressure P_(W). Whilethe control results are omitted, as in Example 1, it was possible tocause the brake hydraulic pressure P_(W) to quickly and smoothly followthe hydraulic pressure P_(M) in the master cylinder 8.

[0039]FIG. 5 shows a vehicle hydraulic brake system to which the controlmethod of the second embodiment has been applied. With this brakesystem, a pump 17 as a hydraulic pressure source driven by a motor 16 isprovided in a fluid passage 20 through which a reservoir tank 18 and awheel cylinder 19 communicate, and a solenoid valve 22 is mounted in arelief passage 21 for returning brake fluid from the wheel cylinder 19to the reservoir tank 18 to produce brake hydraulic pressure with thepump 17 alone.

[0040] To a brake pedal 23 as a brake operating member, a spring 24 forproducing a depressing force F is coupled, and a load sensor 25 fordetecting the depressing force as the brake operating force and a strokesensor 26 for detecting the depressing amount are mounted. Also, in thefluid passage 20, a pressure sensor 27 for detecting the brake hydraulicpressure in the wheel cylinder 19 is also mounted. Detection signalsfrom the sensor 25, 26, 27 are entered into a controller 28, and basedon these detection signals, operations of the motor 16 and the solenoidvalve 22 are controlled.

[0041]FIG. 6 shows a flowchart of the control method of the secondembodiment. In this control method, too, the estimate control and thefeedback control are combined, and it differs from Example 1 of thefirst embodiment in that as an input signal of the brake operatingforce, instead of the master cylinder hydraulic pressure P_(M), thepedal depressing force F detected by the load sensor 25 is used.

[0042] That is, in the estimate control, the controller 28 determinesthe rising speed dF/dt of the pedal depressing force F from the inputsignal of the load sensor 25, and calculates the driving force W_(S) ofthe motor by use of the following equation:

W _(S) =C ₃·(dF/dt)  (4)

[0043] Equation (4), too, is formulated experientially from the relationbetween the rising speed dF/dt of the pedal depressing force F and thedriving force W of the motor necessary to produce the required brakingforce. C₃ is a proportional constant.

[0044] On the other hand, in the feedback control, since the pedaldepressing force F cannot be directly compared with the brake hydraulicpressure P_(W), the pedal depressing force F is converted to the brakehydraulic pressure P_(WA) as a target by use of the following equation:C₄ is a proportional constant.

P _(WA) =C ₄ ·F

[0045] The controller 28 calculates the hydraulic pressure difference ΔPbetween the target brake hydraulic pressure P_(WA) and the actual brakehydraulic pressure P_(W) as detected by the pressure sensor 27, and asin Example 1, computes the increment ΔW of the driving force of themotor for the hydraulic pressure difference ΔP with the gain function fof the PID control and outputs it.

[0046] While these control results are not indicated, to the rise of thebrake depressing force F corresponding to the master cylinder hydraulicpressure P_(M) in the graph of FIG. 3A, the brake hydraulic pressureP_(W) followed quickly and smoothly.

[0047] As described above, in the control method for the vehiclehydraulic brake system of this invention, the equation showing therelation between the rising speed of the brake operating force and theapproximate required motor driving force is determined beforehand, and,using the equation, the motor driving force is preset from the risingspeed of the detected brake operating force. By controlling the motordriving force so as to decrease the hydraulic pressure differencebetween the estimated value or actual value of the brake hydraulicpressure, which rises by the motor driving force, the brake hydraulicpressure is brought close to the target value with the preset motordriving force, and only for the remaining hydraulic pressure difference,the motor driving force is controlled with a small control output. Thus,it is possible to quickly and reliably apply brakes while suppressingpulsation of the brake hydraulic pressure.

What is claimed is:
 1. A method of controlling a vehicle hydraulic brakesystem comprising a wheel cylinder, a pump for producing brake hydraulicpressure by supplying brake fluid into said wheel cylinder, a motor fordriving said pump, a fluid passage for bringing said pump and said wheelcylinder into communication with each other, a brake hydraulic pressuredetecting means for detecting the brake hydraulic pressure in said wheelcylinder, a brake operating member, and a brake operating forcedetecting means for detecting the operating force applied to said brakeoperating member, and adapted to detect the brake operating force bysaid brake operating force detecting means and control the driving forceof said motor with the brake hydraulic pressure corresponding to thedetected brake operating force used as a target value, characterized inthat an equation showing the relation between the rising speed of saidbrake operating force and the driving force of said motor required tocause the brake hydraulic pressure to follow the brake operating forceis determined beforehand, and the driving force of said motor is presetfrom the rising speed of said detected brake operating force by use ofsaid equation, and the driving force of said motor is controlled so asto decrease the hydraulic pressure difference between a target brakehydraulic pressure and the brake hydraulic pressure which is estimatedto rise by said preset driving force or the actual brake hydraulicpressure that has been increased by the preset driving force of themotor.
 2. The method of controlling a vehicle hydraulic brake system asclaimed in claim 1 wherein a master cylinder for producing hydraulicpressure corresponding to the operating force applied to said brakeoperating member is provided, and a master cylinder passage for bringingsaid master cylinder and said wheel cylinder into communication witheach other through an on-off valve is provided to transmit the hydraulicpressure produced in said master cylinder by selectively opening andclosing said on-off valve in said master cylinder passage.
 3. The methodof controlling a vehicle hydraulic brake system as claimed in claim 1 or2 wherein to the equation showing the relation between the rising speedof said brake operating force and the required driving force of themotor, the value of the brake hydraulic pressure itself is added as aparameter.
 4. The method of controlling a vehicle hydraulic brake systemas claimed in any of claims 1-3 wherein a master cylinder hydraulicpressure detecting means for detecting the hydraulic pressure producedin said master cylinder is provided, and the hydraulic pressure in saidmaster cylinder as detected by said master cylinder hydraulic pressuredetecting means is used as the brake operating force in said control.